This invention relates to a sealing device for a bearing.
Demands for size and weight reduction and interior space expansion of each automobile have forced automobiles to reduce the space of each engine room thereof. The size and weight reduction of electrical components and engine accessories have been more advanced. An electromagnetic clutch, a compressor, and an idler pulley for a car air-conditioner are not exceptions. However, a reduction in an output thereof due to the size reduction is inevitable. The reduction of the output of the electromagnetic clutch is compensated by acceleration thereof. Thus, the idler pulley is accelerated. Further, demands for enhancing quietness promote the sealing of the engine room and accelerate the raising of the temperature in the engine room. Consequently, these components need to bear high temperature. In addition, these components are often attached to a lower portion of the engine room. Accordingly, while the automobile runs, rainwater or muddy water is likely to be poured onto these components. Thus, high sealing properties are required by rolling bearings for these components.
A rolling bearing for the idler pulley is used in a manner in which an inner ring is provided at a non-rotating side, while an outer ring is provided at a rotating side. A sealing device for such a rolling bearing has a sliding seal portion configured so that a radially outer circumferential edge part thereof is fit to an inner circumferential side of an axial end portion of the outer ring relatively unrotatably therewith, and that a main rubber seal lip formed on a radially inner circumferential side thereof is slide-contacted with an outer circumferential side of an axial end portion of the inner ring. JP-A-2003-194077 discloses an apparatus configured so that a slinger (dust cover) to be fit to the inner ring provided at the non-rotating side is arranged so as to face an axially outer side of such a sliding seal portion thereby to restrain dust or the like from entering the inside of the bearing.
In recent years, operating conditions of automobiles have tended to become more severe. Higher waterproofing property has become desired by a bearing sealing device in consideration of cases where an amount of water to which an automobile is subjected is assumed to be more increased, e.g., where muddy water is splashed on the automobile, and where car wash water is sprayed onto the automobile, or cases where the automobile is used in a water-damaged or submerged state which is found in a recreational vehicle (RV) or the like. An apparatus disclosed in JP-A-2005-282669 aims at improving the sealing property by forming a sub-seal lip (axial lip), which protrudes toward the slinger and slides on the inner surface of this slinger, on an axially outer surface.
However, the apparatus disclosed in JP-A-2005-282669 has the following problems.
(1) A sub-seal lip is added to the apparatus in addition to a main seal lip. Thus, frictional sliding parts between the inner and outer rings are increased. Consequently, bearing torque is increased. Accordingly, there is a fear that this may be a hindrance to high-speed rotation performance. More particularly, when an axially exposed thread of the sub-seal lip is increased to enhance the waterproofing property, the sliding friction of the seal lip is further increased. Thus, the problem of increase in torque becomes marked.
(2) In the apparatus disclosed in JP-A-2005-282669, a distal end surface of the sub-seal lip is formed to be flat. The sub-seal lip is slide-contacted with the slinger on the distal surface thereof by being radially outwardly inclined. According to such a structure, when the sub-seal lip is elastically deformed by a centrifugal force due to the rotation of the outer ring, the distal end surface thereof is easily floated up from the slinger. Even in a relatively low speed rotation state, the sealing ability of the apparatus is easily deteriorated. More specifically, in a case where a vehicle runs while being submerged in a river, even when the running speed of the vehicle is low, the sealing property of the sub-seal lip is easily impaired. This is likely to lead to a disadvantage that water filled around the bearing rapidly infiltrates thereinto.
Further, sealing devices for a bearing are disclosed also in, e.g., JP-A-2005-325924, and JP-A-11-230279.